They were casualties of Spanish pressure against the revolutionary Katipunan and/or its Rizal-rounded parent organization La Liga Filipina.

Not all this grab-bag of sacrificial patriots were really firebreathing revolutionaries. But the (serious) divisions among Filipino activists and revolutionaries were of small import to the Spanish, who (as the 13-strong martyr batches suggest) went in for the wholesale school of repression.

Perhaps most notable in this day’s batch was Francisco Roxas, one of the Philippines’ wealthiest men. Despite his liberal sympathies, he’d refused the more radical Katipunan’s shakedown for financing, only to have that organization vengefully place his name on a membership list the Spanish were sure to find. (Roxas maintained his innocence, but accepted his unsought martyr’s crown and never betrayed his fellows.)

Two photos of the 13 martyrs’ execution, from this page, with plenty of other undated executions.